This invention relates to a pattern estimation method for measuring the size of a resist pattern during optical lithography employed in the manufacture of a semiconductor device. It also relates to a pattern forming method for determining a development interrupting period for forming the resist pattern.
In optical lithography employed in the manufacture of a semiconductor device, it is important to form an accurate resist pattern. To this end, the prior art employs a method for executing developing period control and size measurement by providing a monitor pattern different from a device pattern and monitoring the intensity of light reflected from the monitor pattern during development or after development.
Japanese Patent Application KOKAI Publication No. 10-300428, for example, discloses a method using a monitor pattern whose element pattern is different from that of a device pattern. In this method, however, a pattern that shows a greater change in size with lapse of development time than the device pattern is used as the monitor pattern, and only this monitor pattern is monitored. Accordingly, when defocusing occurs in an optical system for exposure, a characteristic difference will occur between the device pattern and the monitor pattern. This interrupts accurate developing period control and size measurement.
Further, there is a case where variations will occur in the intensity of reflected light during development, or where lots of time is required until a development interrupting liquid is supplied after the termination of monitoring. If in such a case, a control method for monitoring variations in the intensity of reflected light during development, and stopping development when the measured intensity reaches a threshold value is employed, it is difficult to accurately determine the actual development time period.
With the advance of techniques for refining the size of LSIs, more and more accurate size measurement is required during developing a resist. As afore-mentioned, the method for using a monitor pattern whose element pattern is different from that of a device pattern to measure the size of a resist pattern is disadvantageous in that accurate measurement cannot be realized when defocusing has occurred in an exposure optical system.